The NHS is not insurance, it’s universal healthcare for everyone and is free for those who qualify for it (this includes people on a spousal visa - for which you pay an NHS levy). There’s no such thing as a ‘pre-existing conduction’ on the NHS - everything is treated, regardless of your medical history.
If he needs long-term care in an NHS hospital, that will be free on the NHS, but things like care homes have to be paid for yourself (it’s not the NHS). Some people may be entitled to help with care home costs from the government, but I don’t know the details regarding visa holders - that may come under entitlement to government benefits, not the NHS.
For example, my grandmother needed a hip replacement and was in hospital for several months afterwards - the operation and all the hospital care was free, but when she later went into a care home, she had to pay high weekly fees to live there, which were not covered by the NHS, and instead were partly covered by renting out her house, but my parents had to use some of their money as well.
Sent from my iPhone using Tapatalk